1. Field of the Invention
The present invention relates to an oxide superconductor used in a transmission and distribution wire, a power cable, an equipment lead wire, a magnet wire, and a magnetic shield and a method of manufacturing the same and, more particularly, to an oxide superconductor capable of supplying a large current with zero resistance or small alternating-current loss.
2. Description of the Related Art
An intermetallic compound such as NbTi, Nb.sub.3 Sn, Nb.sub.3 Al, or V.sub.3 Ga and a metal such as Nb or Pb are used as superconductive magnets, magnetic shields, coaxial cables, and cavities by utilizing an ultra low-temperature refrigerant such as liquid helium. These metallic materials, however, are limited as resources. In addition, helium is used to increase cost, which limits the range of practical applications.
To the contrary, some substances which can be rendered superconductive at low critical temperature (Tc) by inexpensive refrigerants have been found, and extensive studies on practical use of such substances in a variety of applications have been actively made.
As the high Tc materials described above, La.sub.2-x Ba.sub.x CuO.sub.4 and La.sub.2-x Sr.sub.x CuO.sub.4 oxide superconductors have critical temperatures of 30.degree. to 45.degree. K.; a Y(Dy, Er, Ho)Ba.sub.2 Cu.sub.3 O.sub.7-.delta. oxide superconductor has a critical temperature of up to 95.degree. K.; Bi-Sr-Ca-Cu-O based oxide superconductors such as Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8 and Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 oxide superconductors have critical temperatures of 80.degree. to 110.degree. K.; and Tl-Ba-Ca-Cu-0 based oxide superconductors such as Tl.sub.2 Ba.sub.2 CaCu.sub.2 O.sub.8, Tl.sub.2 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 and TlBa.sub.2 Ca.sub.2 Cu.sub.7 O.sub.8.5 oxide superconductors have critical temperatures of 90.degree. to 125.degree. K. These oxide superconductors are manufactured as follows. A powder of each superconductor is kneaded with an organic binder to obtain a paste, and the paste is directly extrusion molded or screen-printed. Alternatively, the powder of each superconductor is filled in an Ag pipe or the like, and the pipe is elongated to obtain a conductor having a desired shape.
In a superconductor, a metal stabilizing material is combined with a superconductor molded body to cope with a so-called quench phenomenon in which a superconductive state is lost. For the same purpose as in the oxide superconductor, it is proposed to combine a metal stabilizing material with an oxide superconductor. When the superconductive state is lost, the oxide superconductor becomes an insulator, and it is difficult to conduct heat or electric power to the metal stabilizing material. For this reason, a quench phenomenon more easily occurs. In particular, in alternating-current energization, heat may often be generated by a hysteresis loss. It is very important to appropriately provide a countermeasure against the quench phenomenon of the oxide superconductor.
An oxide superconductor is generally brittle and its crystal has a laminar structure subjected to cleavage. The oxide superconductors tend to crack in installation works. In addition, when an oxide superconductor is used for a magnet, a Lorentz's force acts on the oxide superconductor to crack an oxide superconductor layer. As a result, a critical current density (Jc) is undesirably degraded. Furthermore, since the oxide superconductor has a laminar perovskite crystal structure, crystal anisotropy is strong, and a current flows in a direction parallel to the a-b plane. In order to obtain a high critical current density (Jc), the crystal must be oriented such that its C-axis is perpendicular to a current energization direction. However, since the crystal of the oxide superconductor thus manufactured tend to be oriented randomly, a sufficiently high critical current density Jc cannot be obtained.